Valves are known which introduce a gas inside a plastic body during its formation by pinching the plastic material to create an orifice through which to introduce the gas.
For example, U.S. Pat. No. 6,217,817 and Japanese Patent 2006-192907 describe a plastic body that is pierced by a needle through which the gas is introduced in the plastic body.
The needles are small diameter elements that are useful when the plastic is hard, such as in plastic bottles, but useless if the plastic is not set, as they are blunted.
U.S. Pat. No. 3,978,881 discloses a valve in which the gas is introduced perpendicular to the valve body, so that the device occupies a size too large to allow fitting it in a mould with the actuation area, for introducing gas and cutting the plastic, being within the part cavity.
To solve the aforementioned drawbacks of the state of the art, a description is provided of the following invention of a valve and the method for using it to introduce a gas and punch orifices in plastic in moulds used for making hollow footwear soles. The valve is linearly actuated and includes a helical spring and a stop, such that the valve body head seals against a seat in the valve casing. Its configuration is thus simple, inexpensive and reliable, while the method is efficient as it is performed during the processing cycle of the plastic.